Heat oven to 350°F. Line a 13x18-inch rimmed sheet pan with parchment.
Whisk flour, cornstarch, baking soda, and fine salt in a large bowl.
Stir melted butter with brown sugar and granulated sugar until smooth and glossy.
Whisk in eggs and vanilla until fully combined.
Fold dry mixture into the wet ingredients just until no dry spots remain.
Stir in most of the chocolate chips, reserving a small handful for topping.
Spread dough onto the pan and press evenly into the corners.
Scatter reserved chips over top and sprinkle with flaky salt if using.
Bake 16–20 minutes until edges are deep golden and center looks set.
Cool 15 minutes in the pan, then slice into bars and serve.
Notes
Try swirling 1/3 cup warmed peanut butter over the dough before baking, or fold in 1/2 cup toasted walnuts. Store bars airtight at room temperature for up to 3 days, or freeze up to 2 months.This recipe is an original creation inspired by classic Sheet Pan Chocolate Chip Cookies flavors. All ingredient ratios and instructions are independently developed.